While carrying out flexibility analysis of one of our existing Boiler Feed
Water (BFW) lines operating at 74 kg/cm(superscript: 2) pressure (design
pressure 90 kg/cm(superscript: 2) ) and 182 deg C following are the
salient features of the line :

The line was installed around 20 years back by a consultant. The
flexibility analysis report of that time shows maximum displacement as
128 mm in the axial direction and corresponding transeverse & vertical
displacements are 108 and 31 mm respectively. The whole line is
resting on the spring hangers. The specifications of the hangers are not
available now.

Later on the length of the line on the upstream side was increased and
the operating temperature remained same. The spring hangers provided at
certain locations were found damaged apparently due to excessive
displacement.The pipe at these locations got sagged and now resting on
the pipe rack at around 1 1/2 ft below original position.

This line with modified layout was analysed using CAESAR II with new
hanger as recommended by the s/w. The deflections at these points(where
spring aer found brocken) were as high as 162 mm and 145 mm in axial
and transverse directions respectively.

In order to solve above problem it was tried to provide cold spring(
cut short of 50 mm) in the piping between Node Nos 392 & 395. In this
configuration the deflections came down to the level of 80-90 mm at
spring hanger locations.

Many other options like providing expansion loops, anchors etc. to bring
down the displacement were tried out, however, they didn't yield
satisfactory result.

My queries are as follows :

What is the maximum limit for such displacements.

Of the following methods, which method should be used for the analysis
of above case & why :
a) By using cut-short(material -18) for cold spring or
b) By changing the Alpha tolerance as 1.1 & setting the first available
temp. field for this segment as -1.

Is there any problem in providing cold spring alongwith spring
hangers?

What should be the procedure / sequence for installation of such
piping.


I would be thankful, if anybody could answer to above queries. The input
file is enclosed herewith for the reference

Should anybody require further details, please feel free to contact.